Noticed water dripping from your air conditioning unit? A leaking AC is one of the most common faults we're called out to fix across Essex, Hertfordshire and London. The good news is there are several known causes, and once diagnosed, most are straightforward to repair.
In this guide, we'll walk you through the most likely reasons your air conditioning unit is leaking water, what you can safely check yourself, and most importantly when it's time to call in a qualified engineer. Left untreated, a water leak can cause damage to your walls, ceilings and electrics, so it's worth acting quickly.
📋 In This Article
Is It Normal for an Air Conditioning Unit to Produce Water?
Some moisture production is completely normal. Air conditioning systems work by drawing warm air from your room across cold evaporator coils. As the warm air contacts the cold surface, condensation forms, similar to the droplets that appear on a cold glass of water on a warm day.
Under normal operation, this condensation is collected in a drain pan and safely channelled away through a condensate drain pipe. You may notice a small amount of water dripping from the outdoor unit during operation, this is usually nothing to worry about.
A small amount of water dripping from the outdoor unit is normal, especially in warm or humid weather. The problem arises when water drips or pools from the indoor unit, or when the volume of water is excessive.
If you're seeing water dripping from the indoor wall-mounted unit, pooling around the unit, or staining your ceiling or walls, that's a sign something has gone wrong and needs attention. The Chartered Institution of Building Services Engineers (CIBSE) recommends having any unusual moisture or water leaks investigated promptly to avoid secondary damage.
The 6 Most Common Causes of a Leaking AC Unit
When we attend a callout for a leaking air conditioning unit, these are the faults we find most frequently:
Blocked Condensate Drain Line
The most common cause. Dirt, dust, algae and mould can clog the drain pipe over time, causing water to back up and overflow.
Frozen Evaporator Coil
If airflow is restricted, the coil can freeze. When the ice melts, it produces more water than the drain pan can handle.
Dirty or Blocked Air Filter
A clogged filter restricts airflow, leading to ice build-up on the coil and subsequently excess water when it thaws.
Low Refrigerant Levels
Low refrigerant causes pressure to drop, which can freeze the coil and result in water leaking when the ice melts. This requires a certified engineer to fix.
Damaged or Rusted Drain Pan
On older units, the condensate collection tray can corrode, crack or warp causing water to drip rather than drain correctly.
Improper Installation
If the unit wasn't installed correctly, particularly if it's not level - water may not drain properly and will overflow from the pan.
Understanding the cause is the first step. Some of these, like a dirty filter, you can address yourself. Others, such as low refrigerant or a damaged drain pan, require a qualified engineer. The Health and Safety Executive (HSE) confirms that handling refrigerants requires F-Gas certification. Attempting this without qualifications is illegal in the UK.
What You Can Safely Check Yourself
Before calling an engineer, there are a few simple checks you can do safely. These won't require any tools or technical knowledge but always turn off your air conditioning unit at the wall before inspecting it.
Always switch the AC unit off at the isolator switch before checking anything. Never attempt to open the unit, handle refrigerant lines, or work on any electrical components yourself.
- Turn off the unit immediately
Switch the AC off at the wall or isolator switch. Running a leaking unit risks water reaching electrical components, which is dangerous.
- Check and clean the air filter
Most wall-mounted indoor units have a removable filter panel at the front. If it's clogged with dust and debris, gently remove it, clean it under warm running water, let it dry fully, and refit. A clean filter restores airflow and may resolve the issue.
- Look for obvious ice on the indoor unit
If you can see ice or frost forming on the unit, this confirms a frozen coil. Leave the unit switched off for several hours to allow it to thaw, then check if the filter was the cause.
- Check the drain pipe (if accessible)
If the condensate drain pipe exits through an external wall and is accessible, check it isn't visibly blocked or kinked. Do not attempt to dismantle anything! If it looks blocked internally, call an engineer.
- Check the unit is level
If the indoor unit appears to be tilting downward toward the room (rather than slightly toward the wall), poor installation may be causing water to flow the wrong way. This will need a professional to re-mount the unit correctly.
Most manufacturers recommend cleaning your air filter every 4-6 weeks during periods of regular use. A clean filter is the single most effective thing you can do to prevent faults including water leaks.
If the steps above don't resolve the issue or if you're not comfortable checking anything yourself, the next step is to contact a qualified air conditioning engineer. Our service and repair team can quickly diagnose and fix the fault, getting your system running normally again.
When to Call a Professional Engineer
Some faults go beyond what you can or should attempt to fix yourself. Call a professional immediately if:
- - Water is dripping onto electrical outlets, wiring or your fuse box
- - The volume of water is large or has caused visible water damage to walls or ceilings
- - You've cleaned the filter but the leak persists
- - You suspect low refrigerant (the unit blows warm air, there's a hissing sound, or ice keeps forming after thawing)
- The drain pan appears cracked, rusted or damaged
- Your unit is making unusual noises alongside the leak
- - The unit is less than 5 years old as a fault this early may be covered under warranty
All our installations come with a 10-year parts warranty and 12 months labour cover, giving you long-term protection. If your Evergreen system develops a fault, we're here to help. Contact us and we'll check your warranty status.
🚨 Need an Emergency Callout?
Water leaking near electrics is an urgent situation. Our emergency callout service covers Essex, Hertfordshire, London and beyond - call us now.
Our engineers are F-Gas certified and fully qualified to handle all aspects of AC repair including refrigerant top-ups, coil cleaning, drain line clearance and drain pan replacement. We'll carry out a full diagnostic inspection and give you a clear, honest assessment before any work begins.
We cover residential properties including homes, bedrooms, loft conversions and conservatories, as well as commercial properties including offices, restaurants, shops and server rooms.
How to Prevent Your AC From Leaking Water in the Future
The best way to avoid a leaking air conditioning unit is regular, professional servicing. Many faults (including blocked drain lines and early signs of refrigerant loss) are easily caught and corrected during a routine service, long before they develop into a full leak or breakdown.
Annual Servicing
We recommend having your air conditioning system professionally serviced at least once a year (ideally in spring, before the summer season begins). During a service and maintenance visit, our engineers will clean the coils, clear the condensate drain, check refrigerant levels, inspect the drain pan, and test the full system for performance. This also keeps your warranty valid.
Clean Your Filter Regularly
As mentioned above, a dirty filter is the most common root cause of AC faults. Clean yours every 4 to 6 weeks during active use (most manufacturers also recommend this in their guidelines). The Energy Saving Trust also notes that well-maintained systems run more efficiently, reducing your energy bills at the same time.
Don't Ignore Early Warning Signs
A small drip today can become a significant water leak within days. Other early warning signs to watch for include reduced cooling performance, unusual smells (mould or mustiness), ice forming on the unit, or the unit cycling on and off more frequently than usual. If you notice any of these, contact us before the problem escalates.
Consider an AC Cleaning Service
Over time, mould, bacteria and dust can build up inside your air conditioning unit, particularly in the coils and drain pan. Our dedicated air conditioning cleaning service provides a deep clean that goes beyond a standard service, improving air quality and preventing blockages that lead to leaks.
Conclusion
A leaking AC unit is rarely something to ignore. The most common causes are a blocked drain line, frozen evaporator coil, dirty filter or low refrigerant are all fixable, but most require a qualified engineer to diagnose and repair correctly. The safest course of action is to switch the unit off, clean the filter if you can do so safely, and call us if the leak persists.
With over 16 years of experience servicing and repairing air conditioning systems across Essex, Hertfordshire, London and Cambridgeshire, we're ready to help. Whether you need an emergency callout or want to book a routine service, get in touch today and we'll have your system working properly again as quickly as possible.
